The objectives of this research project are to illuminate the details of the biologic and macromolecular events leading to malignant transformation as induced by endocrine means. The central biologic model is the estrogen induced Leydig cell tumor of the mouse. The inter-relationship of tumor development, hormone binding and alterations in DNA and RNA metabolism are under investigation. These parameters are also being investigated in endocrine induced regressions of Leydig cells. BIBLIOGRAPHIC REFERENCES: Samuels, L.T., Bussmann, L., Matsumoto, K., and Huseby, R.A.: Organization of Androgen Biosynthesis in the Testis. J. Steroid Biochem., 6: 291-296, 1975. Kurland, G., Christensen, A.K., and Huseby, R.A.: Changes in Fine Structure Accompanying Estrogen-induced Tumorigenesis of Leydig Cells in the Mouse Testis. Cancer Res. 35: 1671-1686, 1975.